The present invention relates to the field of excavation systems, and particularly to the field of excavation systems including tools for excavation by electric pulses.
Among existing excavation tools, there are known in particular excavation tools of the cutter type in which a rotary cutter head, or “cutter”, breaks up the ground in order subsequently to allow the spoil that is obtained in that way to be removed. Cutter type excavation tools are usually used to make trenches in the ground to relatively great depth, up to 200 meters (m), and of thickness that is relatively small compared with said depth, the thickness typically lying in the range 500 millimeters (mm) to 1800 mm. A typical width for the tooling is 2800 mm. One of the advantages of such machines is that they enable such trenches of great depth to be made while complying with rigorous verticality criteria, in particular in order to ensure good continuity between adjacent panels. The trench as a whole is obtained by digging successive panels that are adjacent and juxtaposed.
Nevertheless, a drawback of such excavation tools is that they are not very effective when excavating layers of ground that are particularly hard, and in particular layers of rock. In order to solve this problem, tools have been proposed that excavate by electric pulses, e.g. in published patent applications US 2003/0137182 and EP 1 474 587. Such excavation tools typically include electrodes arranged on a front face of the excavation tool. High-power electric discharges between the electrodes can break up the rock situated directly under the front face in a manner that requires less energy than using a cutter.
Nevertheless, electrically powering the electrodes raises other problems. Even when the tool for excavation by electric pulses also includes an electronic power module for producing discharges of high power but of short duration from an electrical power supply continuously delivering nominal power that is more modest, the power supplied is nevertheless sufficiently high to raise problems of safety for equipment and personnel in the event of the power supply cable breaking in the proximity of the surface.
In order to solve that problem, drilling tools are known, in the specific field of drilling by electric pulses, that include generators driven hydraulically from the surface, e.g. the tools disclosed in published patent applications GB 2 420 358 and US 2010/0000790, and in utility model DE 20 2006 018 980 U1. Nevertheless, although such tools for drilling by electric pulses are well adapted to layers of hard rock, they are less well adapted to excavating layers of softer ground.